[antlr-interest] lexer woes

[Matt Benson]

--- Loring Craymer <lgcraymer at yahoo.com> wrote:

> Setting backtracking in combined grammars only
> affects the parser (again, see the prefixWithSynPred
> code); from the code, though, setting
> backtracking=true in lexer grammars does introduce
> synpreds at all decision points.
> 

>From the code... but try to tool this:
----
lexer grammar EasyLexer;
options {
	backtrack=true;
	memoize=true;
}

Ident
	:	Letter (Letter|Digit)*
	;

fragment
Letter 
	:	'A'..'Z'|'a'..'z'|'_'
	;

fragment
Digit
	:	'0'..'9'
	;

---

Does it work, or have I had too much crack?

-Matt

> --Loring
> 
> ----- Original Message ----
> > From: Gavin Lambert <antlr at mirality.co.nz>
> > To: Loring Craymer <lgcraymer at yahoo.com>; Matt
> Benson <gudnabrsam at yahoo.com>; Antlr List
> <antlr-interest at antlr.org>
> > Sent: Wednesday, March 5, 2008 12:09:41 AM
> > Subject: Re: [antlr-interest] lexer woes
> > 
> > At 11:35 5/03/2008, Loring Craymer wrote:
> >  >> 1) Whether backtracking mode is supported for
> lexers,
> >  >1.)  Yes--see calls to prefixWithSynPred() in
> antlr.g
> > 
> > I think that answer is a little misleading :)
> > 
> > As far as I know, the "backtrack=true" option has
> no effect in the 
> > lexer.  However, backtracking in general is
> supported through 
> > adding your own syntactic predicates.
> > 
> > Note that syntactic predicates can only be used to
> disambiguate 
> > between alts in a single rule -- you can't use
> them to distinguish 
> > between tokens at the top level.  (If you need to
> do that, you'll 
> > have to merge the rules.)
> > 
> > 
> 
> 
> 
> 
>      
>
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